In general, an eco-friendly vehicle may be classified as an electric vehicle, a fuel cell vehicle, a natural gas vehicle, or a hybrid vehicle based on a kind of used power source. Specifically, it is possible to classify a battery based eco-friendly vehicle as a hybrid electric vehicle, a plug-in hybrid electric vehicle, or an electric vehicle based on the capacity of a battery or all-electric range thereof. Among them, the hybrid electric vehicle and the electric vehicle necessarily require a separate charging apparatus for charging a high-capacity battery and are equipped with a vehicle-mounted on-board charger (OBC) capable of charging the battery with a home power source.
As the technique of manufacturing a battery has been advanced more than at an early stage of developing an electric vehicle, the capacity of a high-voltage battery mounted on a vehicle is increased, so that OBC products of 6.6 kW next to 3.3 kW have been on the market. However, in a case of a vehicle equipped with a high-voltage battery of about 50 kWh or more, even though an OBC of 6.6 kW is used, it takes about 8 hours to charge the battery.
To overcome the limitation of the related art, a scheme of providing a plurality of power modules connected in parallel to each other into the OBC to increase rating power of the OBC has been introduced. The OBC including a plurality of power modules connected in parallel to each other performs a charging operation in the order of constant current (CC), constant power (CP) and constant voltage (CV). When the charging operation enters the CV charging section, an output current imbalance phenomenon (load imbalance phenomenon) occurs between power modules.
To overcome the output current imbalance between the power modules during such parallel driving, according to the related art, there have been proposed a droop method and an active current distribution method.
According to the droop method, since the negative input of an output voltage compensator of each power module is a value obtained by adding information about an output voltage obtained by detecting an output current thereto, when the output current is increased, a pulse width modulation (PWM) duty, which is a final output of a controller, is reduced, so that the output voltage is reduced. In this case, when a sensing gain of the output current is high, although a load current distribution property between modules is improved, a variation range of the output voltage is enlarged. Thus, it is required to permit some degree of error in current distribution to narrower the voltage variation range.
According to the active current distribution method, as a direction value of an output current of each power module, an output current value of a representative module or an average value of output currents of all power modules may be used according to the magnitude of a scale constant. By reducing the output voltage direction value when the output current of a corresponding module is great compared with a current direction value, the output current is reduced. However, since information about output currents of all power modules is required to be transferred to a master controller, the configuration is complex and the reliability is deteriorated due to a current sensing error.